IoT-Enabled capacitive ammonia sensor platform for real-time environmental monitoring at room temperature

Abstract

We report a capacitive-type ammonia (NH₃) gas sensor integrated with an internet of things (IoT)-based platform for real-time environmental monitoring at room temperature. This is the first demonstration of a capacitive NH₃ sensor, offering lower power consumption and faster response compared to conventional chemiresistive sensors. The sensor employs a vertically aligned exfoliated graphene oxide (EOG) film (∼4 μm thick) with porous microchannels that enhance dielectric polarization and gas diffusion. Structural analyses confirmed multilayer graphene domains with restored sp² networks, while surface functional groups (C–OH, C[dbnd]O) facilitated hydrogen bonding with NH₃, enabling reversible adsorption–desorption. The EOG sensor showed a rapid response time of 45 s and recovery time of 64 s at 4 ppm NH₃, with high linearity (R² = 0.997) over a range of 0.5–4 ppm and a calculated limit of detection (LOD) of approximately 111 ppb. It also exhibited lower resistance (100 kΩ) and capacitance (33.77 pF), resulting in faster charge polarization and improved response. The sensor data were transmitted wirelessly via Wi-Fi to a Raspberry Pi-based cloud server and visualized using a custom web/mobile interface. This study demonstrates a novel capacitive gas-sensing platform with integrated IoT functionality that offers a promising solution for portable and energy-efficient gas detection systems.